Disposal of material contaminated with radioactive materials or chemically hazardous materials present substantial environmental and economic problems. Burial (land fill disposal) of these types of waste materials involve complex technical and socioeconomic-economic problems. In the case of radioactively-contaminated wastes, a substantial reduction in the volume of the wastes to be disposed is feasible since a large portion of the waste consists of organic material. With chemically hazardous wastes large volume reductions are also usually possible. Various methods have been tested to reduce waste volume, including conventional combustion, and staged and fluidized bed combustion.
Typical of the prior art are described in:
1. "Rocky Flats Plant Fluidized Bed Incinerator", L. J. Meile, et al, Report RFP-3249, Mar. 8, 1982. PA1 2. "Circulating Fluidized Bed Technology", Proc. First International Conference on Circulating Fluidized Beds, Ed. P. Basu, November 1985. PA1 3. "Proceedings of the Eighth International Conference on Fluidized-Bed Combustion, Vol. III", Report DOE/METC-85/6021, March 1985. PA1 4. "1989 International Conference on Fluidized Bed Combustion, FBC--Technology for Today", ASME April-May 1989. PA1 1) high combustion efficiency at relatively low temperature (about 550.degree. C.), resulting in a low-fired ash to enhance actinide recovery (if needed) and the elimination of refractory materials of construction which otherwise would create a secondary waste material when replaced; PA1 2) acids produced during combustion can be neutralized in-situ, as with sodium carbonate media, to eliminate off-gas scrubbing; PA1 3) only a dry filter system is needed since only particulate material and not gases must be removed, with the elimination of the need to process aqueous scrubbing solutions.
The above-cited references are incorporated herein by reference for any teachings of process parameters with regard to fluidization, combustion, filtration, etc.
The known techniques all have disadvantages when applied to radioactive and hazardous wastes. Low level radioactive wastes generally consist of a mixture of items such as contaminated gloves and clothing, contaminated wood and building materials, contaminated oils and lubricants, and miscellaneous other items. Primary concerns in the combustion of these materials is, of course, the retention of all radioactive material with the ash of combustion. These wastes typically contain large amounts of plastics with chlorine-containing compounds; therefore, conditions must be maintained to avoid the formation of volatile chlorides of radioactive elements and/or chlorine-containing organic compounds such as dioxins. Avoidance of the potential for criticality, when fissionable materials are present, is also an important consideration.
As stated above, fluidized bed combustion has been investigated as a means of reducing both the volume and weight of radioactive solid and liquid wastes. Some of the valuable characteristics of fluidized bed combustion with regard to this application are:
Although conventional fluidized bed combustion systems for radioactive wastes have these attractive features, the also have some undesirable features. For example, although the off-gas can be dry, carryover of particles from the bed still requires the use of various separators in the form of cyclones and banks of filters. These devices create higher pressure drops across the system, and add significantly to costs. Probably the most important drawback is the requirement for additional separate vessels, piping and hardware that becomes contaminated with radioactivity and complicates repairs and maintenance. Furthermore, because single fluidized bed reactors do not provide a uniform residence time for particles in the bed, some of the waste residue can be carried out of the bed or discharged before all organic matter has been consumed. Also, any chloride sorbent and oxidation catalyst is not fully utilized in a single bed system with the result that there is additional material for disposal.
Accordingly, it is an object of the present invention to provide a system for the fluidized bed combustion of waste which minimizes components subject to contamination that must be disposed of during maintenance and repair.
It is another object of the present invention to provide apparatus for the complete combustion of waste, such as hazardous chemical and radioactive waste, that permits retention of particulates as well as the in situ neutralization of acids.
A further object of the present invention is to provide a combined multi-stage combustion system coupled with filtration such that improved processing of hazardous waste is accomplished with a reduction of apparatus.
It is also an object of the present invention to provide a unique combination of filtration and staging features that involves a combined fluidized bed filter and staged pyrolysis/combustor.
Another object of the present invention is to provide a multi-staged combustion and filtration system for the desulfurization and regeneration of gases.
These and other objects of the present invention will become apparent upon a consideration of the drawings referred to hereinafter, together with a complete description thereof.